1. Field of the Invention
The present invention relates to a technology for post processing sheets for aligning, sorting, and binding the sheets.
2. Description of the Related Art
A sheet post-processing device is used for, for example, aligning, sorting, and binding sheets after forming images on the sheets in an image forming apparatus. Japanese Patent Application Laid-open No. 2005-314092 discloses a technology for aligning a trailing edge of a sheet using a pair of reference members and discharging an aligned stack of sheets with or without performing binding of the sheets. The reference members are located with a constant interval, receiving both sides of the trailing edge of a sheet.
However, the sides of the trailing edge of the sheet is easily curled compared to the center portion of the trailing edge of the sheet and the amount of curl is larger at the sides than at the center portion, so that a curled side of the trailing edge of the sheet may not be abutted with a reference plane, resulting in insufficient alignment of the sheet. If sheets are discharged without being bound as they are not aligned, the sheets are randomly stacked on a discharge tray, causing a difficulty in sorting sheets.